Effects of changes on temperature and fluorine concentration in the structural, optical and electrical properties of SnO₂:F thin films

Thin films of SnO₂:F (FTO) were deposited on glass substrates using the spray pyrolysis technique. Tin dichloride (SnCl₂·2H₂O) was used as a precursor in the starting solution. The first group of samples was prepared adding ammonium fluoride (NH₄F) to the previous mixture in different amounts with respect to tin weight concentration (F/Sn = 0.05, 0.10, 0.15 and 0.20) and deposited at 475 °C. The second group of films was deposited at different temperatures, from T = 475 to 550 °C with a step of ΔT = 25 °C and F/Sn = 0.15 wt. The fluorine and deposition temperature dependencies cause notable changes in the FTO system. The effects on the structure (phase, crystallite size, and microstrain) were investigated using X-ray diffraction associated with Rietveld refinement. The optical properties were studied using the UV–Visible spectrum, and it was fit using the Drude–Lorentz classical dispersion model. The electrical measurements were obtained by four-point Van der Pauw technique. Also, electrical parameters calculated through the Drude contribution, such as resistivity and mobility, were compared with those found in Hall–effect measurements. The FTO with the best figure of merit was integrated as a transparent electrode in a dye-sensitized solar cell.